1. Field of the Invention
This invention relates generally to combustion or gas turbines, and more particularly to combustion turbines having vane segment support and alignment devices.
2. Description of the Prior Art
Over two thirds of large, industrial combustion turbines (which are also sometimes referred to "gas turbines") are in electric-generating use. Since they are well suited for automation and remote control, combustion turbines are primarily used by electric utility companies for peak-load duty. Where additional capacity is needed quickly, and where refined fuel is available at a low cost or where the turbine exhaust energy can be utilized, combustion turbines are also used for base-load electric generation.
In an electric generating environment, a typical combustion turbine is comprised of four basic portions: (1) an inlet portion; (2) a compressor portion; (3) a combustor portion; and (4) an exhaust portion. Air entering the combustion turbine at its inlet portion is compressed adiabatically in the compressor portion, and is mixed with a fuel and heated at a constant pressure in the combustor portion. Thereafter, the heated air is discharged through the exhaust portion with a resulting adiabatic expansion of the gases completing the basic combustion turbine cycle. This basic combustion turbine cycle is generally referred to as the Brayton or Joule cycle.
As is well known, the net output of a conventional combustion turbine is the difference between the power it produces and the power absorbed by the compressor portion. Typically, about two-thirds of combustion turbine power is used to drive its compressor portion. Thus, the overall performance of a combustion turbine is very sensitive to the efficiency of its compressor portion. In order to insure that a highly efficient high pressure ratio is maintained, most compressor portions are of an axial flow configuration having a rotor with a plurality of rotating blades axially disposed along a shaft and interspersed with a plurality of inner shrouded stationary vanes or vane segments which provide a diaphragm assembly having stepped labyrinth interstage seals.
A major factor in reducing compressor efficiency can be found in misalignment of the vane segments in a turbine with respect to a stationary cylinder assembly along the axis of the turbine. It is generally desirable to closely align the vane segments radially between the inner and outer cylinders of the turbine unit so that aerodynamic drag on the vane segments is minimized. These aerodynamic forces which act normally and tangentially upon the surfaces of the vane segments generate torques and moments that are desirably transferred to the casing of the combustion turbine rather than through the vane segments themselves. Otherwise, these torques and moments tend to knock the vane segments out of alignment. There has thus been a long-felt need in the art for apparatus and methods which transfer forces generated by aerodynamic air currents to a combustion turbine casing rather than through the vane segments of a combustion turbine.
Prior art approaches have utilized vane segments having inner and outer shrouds in a generally low-load environment. This approach utilized a cantilevered vane segment off the outer shroud while permanently fixing the vane segment and shroud to the inner and outer cylinders. However, the prior art approach fails with modern, high-load combustion turbines since the tolerances on the inner and outer cylinders of the turbine do not allow for precision alignment due to the sheer size of the vane segments themselves. Additionally, due to the large sizes of combustion turbines in use today it is impractical and uneconomical to physically remove the vane segments and shrouds from the cylinders in order to manually align the vane segments when aerodynamic forces reduce turbine efficiency. Furthermore, since misalignment of the vane segments in a turbine occurs relatively frequently especially in high-load environments, frequent fine-tuning alignment of the vane segments is impossible with the prior art cantilevered design.
Thus, there is a long-felt need in the art for a combustion turbine having adjustable vane segments between an inner and outer cylinder. Aerodynamic drag created by forces acting normally and tangentially upon the vane segments should be minimized by keeping the vane segments aligned radially between the inner and outer cylinders. Furthermore, the alignment of the vane segments in the combustion turbine should be achieved in an economic and efficient manner in the context of a high-load combustion turbine electric generating environment. It is also desirable to provide methods and apparatus for vane segment alignment which transfers torques and moments created by the aerodynamic flow of heated gases into the inner and outer cylinders and casing of the combustion turbine rather than through the vane segments.